More than 611 Million pieces mail are expected to be mailed Monday, which will be the year’s biggest. US Postal Service will process about 7,000 pieces of mail per second on this day. More than 5 million people are expected to visit a Post Office nationwide on Monday – which is twice the normal number. The Postal Service recommends observing mailing and shipping deadlines to ensure that deliveries are made in time for Christmas: they are Dec. 20 for cards and letters, Dec. 21 for Priority Mail, and Dec. 23 for Priority Mail Express.